Bioinspired skeleton conversion synthesis of rare euphoractine A-type diterpenes from naturally abundant lathyranes was achieved on a gram scale. The conversion route features Tsuji-type allylic acetate reduction, Prilezhaev epoxidation, and BF3·Et2O-mediated tandem cyclization processes. Two natural products euphoractins M and N containing a euphoractine A-type skeleton were first synthesized through functional group transformation. This work offers an effective approach for easy access to the naturally scarce euphoractine A-type framework, suggesting the potential biosynthetic relationship between lathyrane and euphoractine A-type diterpenes from a chemical perspective.